Most authorities agree that the sudden infant death syndrome is multifactorial involving several etiological mechanisms. One identifiable cause in a small number of cases is C. botulinum in which infants and animals show an age-related susceptibility to intestinal colonization by this pathogen. Preliminary studies from our laboratory have recently shown that toxigenic strains of C. difficile may be implicated by an analagous mechanism. The evidence is based on the detection of C. difficile toxin in intestinal contents from 6 to 20 victims of SIDS compared to 0 of 56 infants aged 2-4 months. C. difficile is a recently recrgnized enteric pathogen in man. The toxins produced by this microbe are lethal to experimental animals and our preliminary studies show an age related susceptibility to toxin absorption. We propose to more thoroughly examine this association in victims of SIDS and appropriate controls. The source of specimens will be from the SIDS Institute of Maryland which is a multidiscipline collaborative study designed to examine several potential etiologic mechanisms. Specimens are submitted in code from approximately 80 cases and 20 cases controls annually. The techniques to be used are intestinal contents for C. difficile culture, and sera plus intestinal contents for C. difficile toxin assays. Toxin tests include the traditional tissue culture assay and recently developed ELISA assays. Additional studies will be performed to detect alternative microbial toxins in the intestine using biological assays to detect markers. The primary interest will be the use of cell-free supernatant injected intraperitoneally into infant experimental animals and tissue cultures. Once a marker is detected, an attempt will be made to identify a bacterial source or a virus. On the basis of available information we anticipate that the most likely agents will be C. difficile, other toxigenic clostridia or rotavirus. It should be noted that the only microbial agent sought in the current collarborative study are C. botulinum and chlamydia. Therefore, the present proposal adds a major new dimension to this study.